It's important that you keep the lid on when selling your home...

In addition to other benefits, a one reason for hiring an agent to represent you when listing is to provide distance between yourself and potential buyers, basically creating a firewall to protect your interests. 

Interested buyers and their agents, given an opportunity to speak with an owner, will do all they can to ferret information out of the owner.  If you are ever approached for information, always refer those inquiring back to your agent.  It's best to be clear, firm, and if necessary, repetitive.  "You'll have to speak with my agent".  

A recent example I witnessed...

An owner, after giving a property tour himself, among other things told an interested buyer who had knocked on his door (without an appointment or a Realtor) the EXACT AMOUNT of another offer on the table.  Low and behold, the offer that was subsequently received came in at the same price. The owner potentially cost himself a few thousand dollars.  The buyer was motivated but no one wants to overpay for a property.  The seller's best course of action would have been to politely refuse admittance and suggest he make an appointment with his Realtor, and make himself scarce at that time.  There is also a safety concern here, never admit anyone without an appointment.  

Buyers will rationalize all kinds of reasons to approach owners directly, and while it is discouraged by agents, it is a possibility.  When you are selling a home on your own, you must interact with these people.  When you have representation, you'd best redirect them.  Finding out who their agent is will also help YOUR agent have a talk with the other Realtor and suggest they reign in their clients. 

While it's unethical for agents to approach an owner directly, if you are home during a showing, small talk will ensue and you may give away a few nuggets of information.  The easiest way to keep from giving away too much is to vacate the home during showings. 

When I am representing buyers, I am looking for any information that will bolster their position or help me understand the motivation of the sellers of a property.  It's my job.  Agents are very good at asking innocent questions which elicit a wealth of information.  Small talk may cost you. 

Remember, anything you say to another agent can and will be used against you at the negotiation table. 

Absolutely never tell anyone who isn't looking out for your interests...

...Why you are moving

...What your time frame is

...What your financial situation is

...What your family situation is

Actually, don't tell them anything!  Much will be intuited from your answers. 

Two identical houses, side by side, may sell for very different prices based on the situation of the seller.  If buyers or their agents sniff out the reason, either from the appearance or upkeep of the property, the photos on the walls (or lack thereof!), the missing clothes on one side of a closet, or, most commonly, something they've been told, they will see an opportunity to save money.  You have have a weak negotiating position, a high motivation to sell, but there is absolutely no reason that anyone needs to know it.